In a medium pot cook chopped onion in olive oil over low heat for 5 minutes until start to soften.
Add broccoli florets and stock and bring to a boil, cook for 15 minutes with the lid on.
When your broccoli is cooked through, process the soup until smooth in a food processor in two batches or with an immersion blender in the pot together with blue cheese.
If using a food processor, return the soup to the pot and gently heat it until it simmers, take it off the heat and add the smoked gouda, stir until melted and blended in.
Add salt and pepper to taste after both cheese are blended into the soup, the quantity will depend on saltiness of your cheeses and stock.
Garnish with single cream and nigella seeds if desired and serve immediately.